On 22 Aug 2003 at 10:45, Tom Lane wrote:
> Jan Wieck <JanWieck@Yahoo.com> writes:
> > Shridhar Daithankar wrote:
> >> Umm.. What does FSM does then? I was under impression that FSM stores page
> >> pointers and vacuum work on FSM information only. In that case, it wouldn't
> >> have to waste time to find out which pages to clean.
>
> > It's the other way around! VACUUM scan's the tables to find and reclaim
> > free space and remembers that free space in the FSM.
>
> Right. One big question mark in my mind about these "partial vacuum"
> proposals is whether they'd still allow adequate FSM information to be
> maintained. If VACUUM isn't looking at most of the pages, there's no
> very good way to acquire info about where there's free space.
Somehow it needs to get two types of information.
A. If any transaction is accessing a page
B. If a page contains any free space.
Vacuum needs to look for pages not in A but in B. Can storage manager maintain
two lists/hashes with minimal cost? In that case, all unlocked and not in
transaction pages could be a much smaller subset.
Does it sound bizzare?
Bye
Shridhar
--
Chemicals, n.: Noxious substances from which modern foods are made.
